Russian forces backed by tanks and helicopters occupied a Ukrainian village near the border of Crimea Saturday — escalating already-high tensions on the eve of a vote on whether Crimeans should seek annexation by Moscow.

Ukraine’s military responded by scrambling its air force to the region, as the Foreign Ministry denounced the troop movement as an “invasion” and demanded the Russians “immediately withdraw.”

“Ukraine reserves the right to use all necessary measures to stop the military invasion by Russia,” the ministry said in a statement.

As many as 120 Russian soldiers took over the southern village of Strilkove and a nearby gas plant over fears it would be targeted by terrorists, Ukrainian officials said.

No shots had been fired in the standoff — about 80 miles from Crimea — between the two militaries late Saturday. The foray appears to be Russia’s first move outside Crimea, where its forces have been in control since last month.

In the wake of Russia’s takeover of Strilkove, Sen. John McCain (R-Ariz.) called for military aid to Ukraine. “Ukraine is going to need a long-term military assistance program from the United States,” McCain told reporters following a Senate delegation visit to Kiev.

“When [Ukrainians] ask for some modest means that can help them resist, I believe we should provide it . . . it’s simply the right and decent thing to do.”

As the critical vote neared, two people were killed and dozens injured late Friday in a shootout between Russian separatists and pro-Ukrainian demonstrators in Kharkiv — a hotbed of pro-Russia sentiment.

The referendum was denounced by the government in Kiev as “illegal,” and Western countries are threatening Russia with sanctions if it incorporates Crimea.

On Saturday, Russia stood firm, vetoing a US-sponsored resolution at the United Nations declaring the referendum illegal while China, an ally, abstained.

US Ambassador to the UN Samantha Power said the vote shows Russia is, “isolated, alone, wrong.”